In recent years, in display devices such as liquid crystal displays, plasma displays, organic EL displays, etc., a touch panel in which a position input device, for example, a touch input device is combined with a display device is being widely utilized. This touch panel has a structure in which a display unit is laminated with a touch sensor unit in which a glass plate or a resin-made film having a transparent electrode formed thereon and a glass- or resin-made transparent protective plate are laminated to each other.
In the touch panel, as a method for laminating a display unit with a glass plate or film having a transparent electrode formed thereon and an optical base material such as a glass- or resin-made transparent protective plate, etc., there is a technique using a pressure sensitive adhesive double coated sheet. However, in using a pressure sensitive adhesive double coated sheet, there was involved such a problem that an air bubble is easily entrained. As a technique substituting for the pressure sensitive adhesive double coated sheet, there is proposed a technique for laminating them with a flexible ultraviolet-curable resin composition.
As in an example of the touch panel, in display devices such as liquid crystal display devices, etc., there is proposed a structure in which a display unit, a glass plate having a transparent electrode formed thereon, and an optical base material such as a glass-made or resin-made transparent protective plate are laminated to each other.
In the transparent protective plate of a display device having the above-described structure, a stripe-like light-shielding portion is formed in an outermost edge for the purpose of enhancing a contrast of a displayed image. In the case where the transparent protective plate or the touch sensor unit provided with a transparent plate is laminated with other optical member, for example, a glass plate having a transparent electrode formed thereon or a display unit, with an ultraviolet-curable resin composition, a sufficient ultraviolet ray does not reach a light-shielding area of the ultraviolet-curable resin that becomes a shade of the light-shielding portion by the light-shielding portion, so that curing of the resin in the light-shielding area becomes insufficient. If curing of the resin is insufficient, a problem such as uneven display in the displayed image in the vicinity of the instant light-shielding portion, etc. is generated.
As a technique for enhancing curing of the resin in the light-shielding area, Patent Document 1 discloses a technique in which an organic peroxide is contained in an ultraviolet-curable resin, and after irradiation with an ultraviolet ray, the resultant is heated to cure the resin in a light-shielding area. However, there is a concern that a heating step damages a liquid crystal display device or the like. Furthermore, since a time of 60 minutes or more is required for thoroughly curing the resin by heating, there was involved such a problem that productivity is poor. In addition, Patent Document 2 discloses a technique in which an ultraviolet ray is irradiated from the side of an outer side face of the surface on which a light-shielding portion is formed, thereby curing a resin in a light-shielding area. However, since it is difficult to irradiate an ultraviolet ray from the side face depending upon a shape of a liquid crystal display device, the shape of the liquid crystal display device to which the instant method is applicable was limited.
Then, as for the ultraviolet-curable resin which is used for laminating an optical base material having a light-shielding portion, an ultraviolet-curable resin capable of achieving thorough curing with an ultraviolet ray from one direction even in the light-shielding area in which the ultraviolet ray is shielded by the light-shielding portion was demanded to be developed.